8.4. Integrative Issues

This chapter has discussed the impacts of climate change on the North American
region largely in the context of sector-by-sector assessments of plausible impacts.
Several common characteristics among sectors can be identified, however. Also,
viewed collectively, interactions between sectors and subregions can be assessed,
and insights about the integrated nature of the effects of climate change can
emerge.

8.4.1. Limitations of Climate Scenarios for Regional Analyses

Most impact studies have assessed how systems would respond to climate change
resulting from an arbitrary doubling of equivalent CO2 concentrations. These
so-called 2xCO2 scenarios are limited for regional-scale analyses to the extent
that they inadequately correspond to the spatial scales of variability in North
American natural and human systems. They also do not permit an examination of
the effects of climate variability on physical, biological, and socioeconomic
systems. Very few studies have considered dynamic responses to steadily increasing
concentrations of greenhouse gases. Consequently, important insights about the
ability of systems to respond to changing climate over time are lost. This lack
of information is of particular concern because the ability of natural ecological
systems to migrate often may be much slower than the predicted rate of climate
change. Even fewer studies have examined the consequences of increases beyond
a doubling of equivalent atmospheric concentrations.

8.4.2. Regional Texture of Impacts

All of the potential impacts of climate change exhibit a regional texture.
Variations in the regional distribution of impacts need to be clearly articulated
for policymakers. Failure to do so can lead to misleading impressions about
the potential changes in social welfare as a result of climate change and alternative
policy responses. A simple look at aggregate impacts on U.S. agriculture, for
example, might suggest that climate change is not likely to harm agriculture
enough to significantly affect the overall U.S. economy; policymakers might
be left with the erroneous impression that no policy-relevant problems exist.
Distributional differences emerge, however, upon examination of the regional
texture of agricultural impacts.

Different adaptation strategies and options will be necessary to deal with
these regional and sectoral differences. In areas where production significantly
increases-such as the northern edge of agricultural production in North America-additional
adaptation may be necessary in the development of infrastructure to support
expanded population and transportation requirements associated with growth.
The texture of the distribution of sectors and their biological, physical, and
social components across the North American landscape cannot adequately be captured
at a fine enough scale to be relevant to long-range planning at the present
time; these are essential elements of future assessment needs.

It is also recognized-but poorly understood because of limited research-that
climate change may have some benefits (e.g., it may reduce stress or provide
opportunities) for certain areas or sectors within North America (e.g., expanded
agriculture, reduced heating costs) or have a neutral effect on climate-insensitive
sectors. If one examines any one particular climate impact, it is likely that
there will be "winners" and "losers" either across subregions or within a subregion
(e.g., across demographic groups). Nevertheless, the weight of evidence suggests
that when all potential impacts are considered collectively, every subregion
will incur some negative impacts of climate change.

8.4.3. The Role of Adaptation

Some future climate change is inevitable. Strategies for technological and
behavioral adaptation offer an opportunity to reduce the vulnerability of sensitive
systems to the effects of climate change and variability. Some adaptive strategies
can be undertaken in anticipation of future climate change; others are reactive
and can be undertaken as the effects of climate change are realized.

Four points must be kept in mind when considering the extent to which adaptive
strategies should be relied upon. First, adaptation is not without cost. Scarce
natural and financial resources must be diverted away from other productive
activities into adaptive practices. These costs must be carefully weighed when
considering the tradeoffs among adapting to the change, reducing the cause of
the change, and living with the residual impacts. Second, the economic and social
costs of adaptation will increase the more rapidly climate change occurs. Third,
although many opportunities exist for technological and behavioral adaptation,
uncertainties exist about potential barriers and limitations to their implementation.
Fourth, uncertainties exist about the efficacy and possible secondary effects
of particular adaptive strategies.

8.4.4. Water as a Common Resource Across Sectors and Subregions

Water is a linchpin that integrates many subregions and sectors. Available
water supplies will be directly affected by climate change, but they also are
affected by changes in demand from the many sectors that rely upon the water.
Water is a scarce resource used in the agriculture, forest, and energy sectors.
It is used in urban areas and in recreational activities. It also is essential
for the survival of wetlands, nonforest ecosystems, wildlife, and other ecological
systems.

Assessments of the potential impacts of climate change and variability on any
of these systems and sectors must account for the inherent competition for water
supplies and the need for water of varying qualities in various activities.
For example, in an assessment of the potential impacts of climate change on
agriculture, an assumption that farmers will be able to adapt to changing climatic
conditions through a reliance on irrigation is valid only to the extent that
water is available under future climate scenarios. In many cases, the scarcity
of available water supplies will increase because of the direct effects of climate
change on water, as well as increased demands for available water supplies.